Composite components are frequently produced using radically crosslinkable polymer compositions based, for example, on unsaturated polyester resins (UP resins). Unsaturated polyester resins are obtainable by polycondensation of dicarboxylic acids or dicarboxylic anhydrides with polyols. The radically crosslinkable polymer compositions further comprise monomers having ethylenically unsaturated groups, generally styrene. Styrene is added to the radically crosslinkable polymer composition in order, for example, to dissolve the crosslinkable polymer and to ensure that the radically crosslinkable polymer composition is a fluid material. As further constituents, the radically crosslinkable polymer compositions often further comprise fiber materials such as glass fibers, carbon fibers or corresponding fiber mats (Fiber Reinforced Plastic composites; FPR composites), which lead to reinforcement of the composite components obtainable by curing the radically crosslinkable polymer compositions.
A problem associated with the processing of such radically crosslinkable polymer compositions to composite components is the volume contraction in the course of curing of the polymer composition. In order to reduce the shrinkage on curing, therefore, the radically crosslinkable polymer compositions are admixed with additives known as low-profile additives. Low-profile additives reduce the shrinkage on curing, dissipate intrinsic stresses, reduce microcracking, and facilitate compliance with manufacturing tolerances. The LPAs are typically thermoplastic homopolymers and copolymers of polystyrene, polymethyl methacrylate or polyvinyl acetate, and are used in the form of solid resins. For example, in U.S. Pat. No. 3,718,714 or in DE-A 102006019686, copolymers based on vinyl acetate and ethylenically unsaturated carboxylic acids are recommended as LPAs for the production of composite components based on unsaturated polyester resins. For the production of composite components, EP-A 0075765 recommends radically crosslinkable polymer compositions comprising as LPAs polymers based on vinyl acetate and/or alkyl acrylates, and ethylenically unsaturated fatty acid esters as well.
EP-A 0337931 describes LPAs in the form of redispersible polymer powders based on copolymers of vinyl acetate and Versatic acid vinyl esters for producing composite components at low temperatures.
The polyvinyl ester copolymers hitherto commonplace as LPAs do usually produce a substantial antishrinkage effect, in comparison to polystyrene and polymethyl methacrylate, that are unsatisfactory in terms of pigmentation. Good pigmentation means that the curing of radically curable polymer compositions comprising pigments produces composite components having a uniform colored appearance; in other words, the pigments are uniformly distributed in the components. With poor pigmentation, in contrast, the pigments are not uniformly distributed in the composite components, and an effect occurs which is referred to as marbling.
In order for the LPAs to be able to develop their effect in the radically curable polymer compositions, the LPAs must be present in dissolved form. A disadvantage is that the dissolution of the commonplace LPAs takes a very long time. For this reason, the LPAs are commonly first dissolved in styrene, in a separate, time-consuming process step, and then incorporated in this form into the radically curable polymer compositions. A further problem is posed by the storage of the LPA-containing styrenic solutions, since such solutions have a tendency toward uncontrolled polymerization, and, moreover, measures must be taken in order to prevent premature polymerization.